That's a lie
The cup is IN HIS HAND! They thought it would be funny to do, and now they are getting heat for it.
Complain to CBS, and demand that someone be PUBLICALLY FIRED for this. This was supposed to be a family show.
1. During song they were singing Justin's repated line was something to the effect that "I'm gonna get you naked by the end of this song."
2. She appeared to be wearing a pastie, and the removable part of her clothes appeared to be attached with velcro---obviously planned.
3. He just stood their with the ripped off clothing in his hand and he stared down at her, making no attempt to cover what he'd uncovered.
4. Justin famously did something similar, which casued a lot of controversy, when he grabbed Kylie Minogue's a$$ during a duet on a Brit awards show, as I remember. There was question then also if it was planned or if Jus just reached for a handful on his own.
So yeah, it's pretty laughable for him to suggest it was a costume malfunction.